Vane-type camshaft phasers for varying the timing of valves in internal combustion engines are well known. A typical phaser comprises a rotor attached to a camshaft and a stator surrounding the rotor and driven in time with an engine crankshaft. The phaser is able to vary the angular position of the rotor with respect to the stator and thus to vary the valve timing imposed on the camshaft with respect to the crankshaft and pistons.
A phaser typically includes a spring for biasing the rotor in a specific angular direction with respect to the stator, for example, in a timing-retarding direction. In the prior art, the coiled spring has a first tang (referred to herein as the “stator tang”) extending into contact with a fixed stop, such as for example a slot, protruding pin or bolt head grounded to the stator, thus anchoring one end of the spring to the stator. A second tang (referred to herein as the “rotor tang”) at the opposite end of the spring coil is grounded to the rotor by attachment directly thereto, of by attachment to a component, such as a target wheel, which is grounded to the rotor. Because the first and second tangs are spaced apart axially of the phaser, the spring produces torque on the rotor not only about the phaser axis but also about a second axis transverse to the phaser axis. This second torque amounts to a cocking of the rotor within the stator, which cocking selectively urges portions of the rotor vanes preferentially against the stator front and rear covers, thereby causing unequal wear on the rotor vanes. As presently installed in a substantial number of different camshaft phasers on the market today, this spring orientation causes wear and cocking of the rotor that can eventually lead to high levels of leakage between the advance and retard chambers, affecting phaser control directly, and also can lead to unacceptably high parasitic losses in total engine oil flow.
In particular, the cocking action lifts the lower rotor surface of the large vane containing a locking pin assembly. Subsequent wear on the other vanes causes a widening clearance between the large vane face and the stator rear cover, thereby affecting control of the locking pin itself as well as an undesirable free flow of oil past the locking pin vane.
What is needed in the art is an improved spring position for the biasing spring of a camshaft phaser wherein wear patterns of the phaser rotor are altered or reduced to reduce parasitic leakage between advance and retard chambers.
It is a principal object of the present invention to reduce leakage between advance and retard chambers due to rotor wear in a camshaft phaser.